1. Field of the Invention
The present invention relates to an ultrasonic probe and an ultrasonic diagnostic apparatus using a micromachining ultrasound transducer (MUT).
2. Description of the Related Art
An ultrasonic probe drives a plurality of vibration elements to radiate ultrasonic waves therefrom. The ultrasonic waves reflected by a subject or the like are received by the plurality of vibration elements.
Phase-controlled ultrasonic waves are superposed for delay control of the plurality of vibration elements to form an ultrasonic beam. At this point, the width of the vibration elements is designed to be about half of the wavelength of a center frequency to prevent a reduction in the directivity of the vibration elements.
For example, when the ultrasonic beam is inclined 30 degrees with respect to the center, its sound pressure decreases by about 3 to 6 dB as compared with sound pressure in a 0-degree direction. One reason for this is that the ultrasonic waves are not equally radiated in all directions from the vibration elements. Ultrasonic waves of higher frequencies are more sharply radiated forward and are not uniformly radiated over a wide range. Therefore, in the case of, for example, a harmonic imaging method using a high frequency band, the width of the elements has to be reduced to suit the frequency used. However, a reduced width of the elements decreases production yield or decreases power per element.
In this connection, the vibration element includes an element made mainly of piezoelectric ceramics or a capacitive micromachining ultrasound transducer (cMUT). cMUT is manufactured by processing a semiconductor substrate using a micromachining technique. The element made with piezoelectric ceramics is in the shape of a rectangular parallelepiped, while the cMUT is formed flat. Thus, the ultrasonic radiation surfaces of both types of vibration elements are flat.
Jpn. Pat. Appln. KOKAI Publication No. 2005-210710 describes a technique whereby an array of MUTs formed by flatly arranging a plurality of MUT elements is curved in order to curve the whole ultrasonic radiation surface of the MUT array. The vibration element (MUT element) described in Jpn. Pat. Appln. KOKAI Publication No. 2005-210710 is a flat vibration element.